This invention relates to an axle assembly having multiple wheels at each end of an axle in which one wheel is permitted to rotate relative to the other wheel, and more specifically, the invention relates to a mechanism for locking the wheels together for driving and/or braking both wheels.
Axle assemblies having dual wheels on either end of the axle have been used to increase the load bearing capability of heavy duty vehicles. Typically the pair of wheels on each end of the axle assembly is secured together so that they rotate together about an axis. Some heavy duty vehicles, such as lift trucks, undergo numerous turning maneuvers which wear the tires significantly. The tire wear is caused when the tires scrub, or drag, since the wheels that are secured together must travel different distances at the inside and outside of the turning radius. Tire wear and maintenance on heavy duty lift trucks due to scrub cost thousands of dollars annually per vehicle.
Dual wheel assembly designs have been proposed that permit the wheels to rotate relative to one another to reduce scrubbing during vehicle turns while driving at least one of the wheels to propel the vehicle. Certain driving conditions require that both wheels be driven to provide enough traction to propel the vehicle and its load. Simnilarly, braking force may be required at both wheels to produce sufficient braking force to stop the loaded vehicle. These competing requirements make it difficult to design a dual wheel assembly having all the desired characteristics. Some designs have been developed which utilize a differential gear set between the wheels so that both wheels may be driven. Other designs have provided a second brake assembly slaved off a first brake assembly to provide braking force to both wheels. However, prior art designs do not provide a mechanism that will lock wheels together, which are rotatable relative to one another, for driving and/or braking conditions. Therefore, what is needed is a mechanism that permits the wheels to be selectively locked together to provide increased traction and/or to permit braking force to be applied to both wheels.
The present invention provides a variable engagement mechanism for a dual wheel assembly. The mechanism includes a spindle having a drive axle defining a rotational axis. A first wheel hub is supported on the spindle and coupled to the drive axle for being rotatably driven about the rotational axis. A second wheel hub is arranged adjacent to the first wheel hub and is rotatable relative to the first wheel hub about the rotational axis. In one embodiment, the first wheel hub has a support member extending there from along the rotational axis and the second wheel hub is supported on the support member. First and second friction discs are adjacent to one another and splined to the first and the second wheel hubs, respectively. An actuator forces the friction discs into engagement with one another to permit transfer of torque between the wheel hubs. In this manner, the first and second wheel hub may be selectively locked together.
In another embodiment, the second wheel hub includes an interlocking member. An engagement member is splined to the support member to prevent relative rotation there between and is movable relative to the support member along the rotation axis to an engaged position in which the engagement member engages the interlocking member. In the engaged position the first and second wheel hub are coupled together. A first actuator moves the engagement member along the rotational axis to the engaged position for increased traction or braking. Friction discs may be used between the engagement member and a housing supported by the spindle to provide a braking force to both wheel hubs when they are coupled together.
In yet another embodiment, a friction surface is supported on one of the first and the second wheel hubs. A friction member is movable toward the friction surface along a second axis. A biasing member is interposed between the friction member and the other of the one of the first and the second wheel hubs for forcing the friction member against the friction surface and transferring torque between the wheel hubs. The biasing member may be a passive device such as a spring or an actuator such as a hydraulic piston.
In still another embodiment, a differential assembly is interconnected between the first wheel hub and the second wheel hub. The differential assembly includes a gradual locking mechanism movable between unlocked and locked positions. An actuator moves the locking mechanism and locks the first and the second wheel hubs together in the locked position to prevent relative rotation there between. In this manner, both wheels may be driven while the second wheel is permitted to rotate relative to the first wheel. However, the differential may be gradually locked when increased traction or braking is necessary.
Accordingly, the above inventions provide is a mechanism that permits the wheels to be selectively locked together to provide increased traction and/or to permit braking force to be applied to both wheels.